This invention relates to a novel apparatus for clamping a drill onto a workpiece for precision drilling of a hole at a desired location thereon.
Modern production methods often require precision drilling in cramped work locations. It is not feasible to use conventional precision drilling systems in such locations because prior art precision drilling systems typically require a substantial amount of working space to precisely secure the drill system to the workpiece. Indeed, some conventional portable drilling systems require that the drill be positioned against the workpiece template and rotated 90.degree. in order to lock the drill into position. Frequently, modern production methods require precision drilling of holes in areas where a hand drill alone can barely fit. Consequently, with prior art systems, there is frequently no alternative but to drill the required hole manually with an ordinary hand drill. However, such hand drilling is time consuming and tends to result in imprecision and inaccuracy in the location, size and shape of the hole drilled.
One prior art method for precision drilling of holes in a workpiece uses a drill jig. Such prior art devices typically include a sliding member, one or more guide rods and a means for clamping the sliding member onto the workpiece. The drill bit is then inserted between two plates or into an aperture in one of the members. Such an apparatus is disclosed in U.S. Pat. No. 2,556,131 to WOLFSON. Since these types of apparatuses do not include a drill as an integral part of the structure and may have many different separable parts, setting up such a system may be time consuming and complex, and it frequently takes an inordinately long period of time to commence the actual drilling.
Many other types of prior art drill systems combine a drill with a workpiece support member. A bolt and mounting bracket structure may be incorporated in such systems to press the workpiece against the drill bit. However, the disadvantage with these systems are that the bolt typically must be manually turned to press the workpiece directly against the drill bit thereby positioning the bit at the precise location of the hole to be drilled. But, rotating the bolt thereby moving it longitudinally and rotationally against the workpiece can also move the workpiece out of position. Moreover, precise location of the hole to be drilled is often difficult because it is difficult to visually ascertain precisely where the workpiece is contacting tne drill bit. Moreover, as drilling commences and the pressure exerted against the drill bit is reduced, the rotating action of the drill bit tends to move it out of position on the workpiece. This may result in an oval hole or a larger hole than desired. An example of such a prior art device is U.S. Pat. No. 1,407,348 to HEER.
Another type of prior art drilling system combines a simple pair of tongs with a hand drill. A drill is mounted at an end of one of the tongs. At an opposing end of the other tong there is a flat disk which engages an underside of the workpiece. Closing the pair of tongs clamps the workpiece between the drill bit and the disk. However, it is difficult to get precise drilling done with such a system because one hand is required to apply pressure to keep the tongs closed while the other is required to apply pressure to operate the drill. Coordinating both hands in this manner makes operation of such a system awkward. Moreover, the pressure exerted on the workpiece decreases as the drilling operation proceeds. Reduction of pressure during drilling can enable the drill bit to move out of its desired position relative to the workpiece. This can introduce gross inaccuracies in the holes drilled. An example of sucn a drill apparatus is disclosed in U.S. Pat. No. 55,696 to NEVERGOLD.
Still another type of prior art system incorporates a carriage within which is a drill, a hydraulic feed mechanism and a clamping member. The workpiece is clamped within the carriage and tne drill is hydraulically moved against the workpiece and retracted therefrom at the end of the drilling operation. The primary disadvantage with such systems is that they are not portable and typically may only be used on a workpiece before the workpiece is integrated into the finished structure. An example of such a prior art device is disclosed in U.S. Pat. No. 3,041,896 to MAY.
In general, prior art devices are impractical for use in many areas which have limited working space or are relatively inaccessible. Moreover, most prior art precision drilling devices are not portable, and accurate drilling work using prior art devices typically requires that the workpiece be separate from the finished structure in order for it to be properly positioned in the drilling apparatus. In addition, prior art devices tend to be difficult and time consuming to set up properly and do not yield the drilling accuracy required for many modern production methods.